1. Field of the Invention
The instant invention relates to a device for sampling gases and more particularly to a device for periodically taking samples of natural gas from a natural gas pipeline and for passing the samples to a means for storing the gas for later analysis.
2. Description of Related Art
Natural gas typically occurs as a mixture of low molecular weight hydrocarbons obtained in petroleum-bearing regions throughout the world. In the United States, it occurs chiefly in the southwestern states and Alaska. Natural gas is composed primarily of methane. It may also include ethane, propane, isobutane, butane, pentane and hexane which are sometimes referred to as "light liquids," because they may exist in liquid or gas phase, depending on pressure and temperature. Natural gas may also include nitrogen, water, hydrogen sulfide and other fluids.
The content of natural gas varies widely from location to location. Some gas wells produce primarily methane and are referred to in the industry as "dry wells." These wells produce hydrocarbons in commercial quantities and should not be confused with the term "dry hole." A well which is incapable of producing hydrocarbons in commercial quantities is called a "dry hole"; it is typically capped and written off as a loss. Some gas wells produce methane in combination with "light liquids" and perhaps other fluids and are referred to in the industry as "wet wells." The natural gas produced from "dry wells" and "wet wells" is commingled in gathering systems and transmission pipelines. Extraction plants are often located between gathering systems and transmission lines to strip out the "light liquids" and other fluids. Depending on supplies and prices, the extraction plant may or may not be in operation.
Today, natural gas is bought and sold based on volume and heating value. The amount of heat generated by the burning gas is measured in Btu's (British thermal units). Gas from "wet wells" produces more energy in the form of Btu's per volume when burned than does gas from a "dry well." For example, methane, by itself, produces approximately 900 Btu's when burned. If a little ethane is mixed with the methane, the heating value rises to approximately 1000 Btu's. In general, the natural gas industry strives to deliver approximately 1000 Btu gas; however, the heating value can vary significantly, depending on the types and amounts of the "light liquids" present in the natural gas. As a result, both buyers and sellers of natural gas are interested in the heating value, expressed as Btu content, of the gas in order to insure that a fair price is paid for the gas.
The price of natural gas in most industrial applications is based on volume which is adjusted either up or down, based on a Btu factor. Today, it is also common practice for many local utilities to sell natural gas to homeowners based on volume which is adjusted based on a Btu factor. These heating value adjustments are based on actual tests of the natural gas. These tests typically require that samples of the gas be taken in the field and brought to a laboratory for analysis. The heating value of natural gas is typically analyzed with a calorimeter.
In order to analyze the heating value of the natural gas in a pipeline, sampler systems, such as that shown in FIG. 1, have been developed. FIG. 1 is a schematic of the present invention with ancillary operating equipment attached. As shown in FIG. 1, natural gas from a pipeline passes from the pipeline (not shown) to the sampler assembly, generally labeled 1, through an inlet pipe 2. Inlet pipe 2 is connected to a sample pump 3. The natural gas entering sample pump 3 through inlet pipe 2 enters sample pump 3 at the natural gas pipeline pressure. This pipeline pressure varies from a low of about 100 pounds per square inch ("psi") to higher than 1800 psi but is typically about 1100 psi.
A portion of the natural gas from inlet pipe 2 passes through sample pump 3 and exits sample pump 3 through outlet pipe 4. Outlet pipe 4 is connected to regulator/relief valve 5. Regulator/relief valve 5 drops the natural gas pressure from outlet pipe 4, which is at pipeline pressure, to a value of about 60-70 psi and passes the natural gas under the reduced pressure out of regulator/relief valve 5 through connecting pipe 6. The regulator/relief valve 5 includes a relief valve to vent excessive pressures to the atmosphere.
Connecting pipe 6 connects regulator/relief valve 5 to timing valve 9. Timing valve 9 is opened and closed by a solenoid 10 that is in turn controlled by a timer 11. Timer 11 may be a simple device that periodically activates solenoid 10 to open and close timing valve 9. However, the preferred form of timer 11 is a device that reacts to the volume of gas passing through the natural gas pipeline to activate solenoid 10 to open and close timing valve 9 so that periodic samples, corresponding to the flow rate through the pipeline, are taken by sample pump 3.
When timing valve 9 is opened under the direction of solenoid 10, natural gas flows through the inlet pipe 2, the sample pump 3, the outlet pipe 4 to the regulator relief valve 5 from connecting pipe 6 through timing valve 9 through sample pump pipe 12 to diaphragm motor 7 of sample pump 3. When, under the direction of solenoid 10 and timer 11, timing valve 9 is closed, timing valve 9 is vented to the atmosphere so that natural gas under pressure in the diaphragm motor 7 of sample pump 7 is vented to the atmosphere through timing valve 9. The opening and closing of timing valve 9 under the ultimate direction of timer 11 activates the sampling process that samples the natural gas presented from inlet pipe 2 and passes the samples to a sample cylinder 14 through sample cylinder pipe 13.
Sample pump 3 takes a small portion of natural gas from inlet pipe 2 and, when activated by the opening of timing valve 9, moves that small sample from sample pump 3 through sample cylinder pipe 13 to sample cylinder 14. Sample cylinder 14 then contains the accumulation of samples taken from the natural gas pipeline. Sample cylinder 14 may be removed and taken to a laboratory where its contents can be analyzed for the Btu content which, as discussed above, affects the price of the natural gas.
A typical prior art sample pump 3 sold by the Welker Engineering Company as model GSS-4 is shown in schematic cross section in FIG. 2. The sample pump 3 shown in FIG. 2 contains a diaphragm case 200 that is attached to sample pump pipe 12. A body 202 is attached to diaphragm case 200 opposite sample pump pipe 12. Body 202 is in turn connected to manifold 204 opposite diaphragm case 200.
Diaphragm case 200 contains two parts, a pressure chamber cover 206 and an ambient atmosphere chamber cover 208. Pressure chamber cover 206 and an ambient atmosphere chamber cover 208 are both usually substantially bowl shaped and each has an annular outward projecting flange 210 that extends away from the edge of the covers 206, 208 at substantially a right angle to the central axes of the covers 206, 208. Covers 206, 208 are placed in contact with each other at flange 210.
A flexible gas tight diaphragm 212 is placed between the respective flanges 210 of covers 206, 208 as covers 206, 208 are brought into contact with each other along the respective flanges 210. A series of bolts 214 and nuts 216 extend through holes in flange 210 located at equally spaced locations around the periphery of covers 206, 208. The plurality of bolts 214 and nuts 216 combine to bring both sides of covers 206, 208 into tight contact with each other and diaphragm 212 to form a gas tight seal between diaphragm 212 and the ambient atmosphere at flange 210.
A typical prior art sample pump will have about eighteen (18) bolts 214 and nuts 216 holding covers 206, 208 together. When covers 206, 208 are to be joined in assembling or servicing the sample pumps, flanges 210 on covers 206, 208 are abutted and each of the eighteen bolts must be passed through an aligned hole in each flange 210 of cover 206, 208. In addition, the bolt 214 will also preferably pass through a hole in diaphragm 212 corresponding to the holes positioned in the flanges 210. Thereafter, each bolt 214 has a nut 216 placed on its end that is rotated by a wrench until it is tightened. During this process, it is easy for the bolts or nuts to become dropped or misplaced. This is clearly a problem to be avoided.
An additional problem related to this flange and nut and bolt joining system is that if a single bolt 214 and its corresponding nut 216 are not securely tightened, the gas tight seal at that point may be broken. As will be explained hereafter, it is important to the operation of sample pump 3 that a gas tight seal be maintained around flange 210.
A further problem with the bolt and nut connection system of the prior art sample pumps described above is that a wrench is required to disassemble and reassemble the diaphragm case 200 of the sample pumps 3. Often a wrench to fit the bolts 214 and nuts 216 is difficult to locate or unavailable. Also, during the disassembly and reassembly process the wrench may be dropped or misplaced. Clearly, it is desirable to eliminate the need to have to use a wrench to assemble or disassemble a sample pump.
A gas tight pressure chamber 218 is formed between pressure chamber cover 206 and diaphragm 212. Because pressure chamber 218 is gas tight and in fluid communication with sample pump pipe 12, the pressure in sample pump pipe 12 will be the pressure in pressure chamber 218.
An ambient atmosphere chamber 220 is formed between ambient atmosphere chamber cover 208 and diaphragm 212. A vent 222 connects ambient atmosphere chamber 220 and ambient atmospheric pressure so that air within ambient atmosphere chamber 220 is at the ambient atmosphere pressure.
A planar metal plate 226 abuts diaphragm 212. A spring 224 is placed within ambient atmosphere chamber 220 between ambient atmosphere chamber cover 208 and plate 226. Spring 224 biases plate 226 into contact with diaphragm 212 and aligns plate 226, in spring 224's unstressed configuration, with the plane formed through flanges 210 when covers 206, 208 are connected by bolts 214 and nuts 216.
Base 204 is fluidly connected to and communicates both with inlet pipe 2 and sample cylinder pipe 13 as described above. Some natural gas entering sampler pump 3 through inlet pipe 2 passes through connecting passageway 221 to outlet pipe 4 where it passes to regulator/relief valve 5 as described above. Some of the natural gas passes to a sample chamber 228 in body 202.
As described above, some natural gas leaving sample pump 3 through outlet pipe 4 eventually enters pressure chamber 218 through sample pump pipe 12 when timing valve 9 is opened under the direction of timer 11. When timing valve 9 is opened, natural gas passes through timing valve 9 into pressure chamber 218 of diaphragm case 200 to activate the diaphragm motor 7. In the chamber 218, the natural gas contacts diaphragm 212 that provides a gas tight barrier across diaphragm case 200. The pressure of the natural gas against diaphragm 212 causes diaphragm 212 to contact plate 226 and move both itself and plate 226 away from sample pump pipe 12 against the bias of spring 224.
Referring to FIG. 3, body 202 contains a hollow cylinder 232 that is open at one end and substantially closed at the other. A sample chamber 228, as will be described in detail hereafter, is formed at the substantially closed end of cylinder 232.
A piston 234 is placed in hollow cylinder 232. An elongated piston rod 236 connects plate 226 to piston 234. Piston 234 is cylindrical, usually having a diameter larger than the diameter of piston rod 236 but slightly smaller than the diameter of hollow cylinder 232. Piston 234 moves within cylinder 232 and abuts a cylindrical elastomeric plug 238 having a diameter about equal to the diameter of piston 234. Plug 238 has a concave depression 240 opposite piston 234.
A gas tight seal 242 is placed around piston 234 within cylinder 232 so that gas within cylinder 232 cannot move out of the open end of cylinder 232 between piston 234 and cylinder 232 past seal 242.
In the prior art device described above, the piston 234 extends into a recess 244 in piston rod 236. Piston rod 236 is connected to the piston 234 by corresponding threads on piston 234 and recess 244. A pin 246 extends through a bore 248 located along the diameter of piston 234. Pin 246 is slightly longer than the diameter of piston 234 and contains a detent 250 at its midpoint. Bore 248 has a recess 252 extending away from bore 248 at a right angle at the midpoint of bore 248 in the neck 249 of piston 234.
A small metal ball 254 is located in recess 252 so that ball 254 extends into bore 248. A small spring 256 is located behind ball 254 in recess 252 to bias ball 254 into bore 248. A threaded stop 257 threadably engages threaded recess 252 to hold the spring 256 and ball 254 in place. When pin 246 is placed through bore 248 until it is centered in bore 248, ball 254 engages the detent 250 in pin 246 to hold pin 246 in position within bore 248.
A shield 258 extends around piston 234 and plug 238 and encases the end of plug 238 opposite piston 234. When pin 246 is in place in bore 248 the ends of pin 246 extend beyond the outer surface of piston 234 into elongated small holes 260 in shield 258. Holes 260 are elongated in the direction of the axis of piston 234. When plug 238 is not compressed by piston 234, as will be described hereafter, the ends of pin 246 contact the edges of holes 260 furthest from concave depression 240. The interaction between holes 260 and pin 246 holds shield 258 in position around piston 234 and plug 238.
As will be explained hereafter, as plug 238 is compressed by piston 234, the ends of pin 246 move within holes 260 from the position farthest from concave depression 240 toward concave depression 240. Ultimately, as plug 238 continues to be compressed, the ends of pin 246 will contact the edge of holes 260 closest to concave depression 240, thereby stopping further compression of plug 238.
This system of attaching the piston rod 236 to the piston 234 has been found to be expensive to manufacture due to the small size of the parts and the intricate work needed to form and assemble the ball 254, the spring 256, the stop 257 and the pin 246. It is clearly desirable to simplify the connection between the plug 238 and the piston 234.
As plate 226 is moved against the bias of spring 224 by the natural gas pressure within pressure chamber 218, piston rod 236 moves piston 234 toward the closed end of cylinder 232. As piston 234 moves toward the closed end of cylinder 232, the concave depression 240 of plug 238 moves into sealing contact with vacuum breaker wafer 231. A kelk spider seal 233 is captured between the wafer 231 and the bottom of cylinder 232. A bore passes through the center of wafer 231 and seal 233 and is aligned with sample outlet 235 in the bottom of cylinder 232. Further movement of piston 234 toward the closed end of cylinder 232 compresses plug 238 and the concave depression 240 against the closed end of cylinder 232. Because the concave depression 240 of plug 238 is pressed into sealing contact with the closed end of cylinder 232 and because plug 238 is made of an elastomeric material, as piston 234 compresses plug 238, the concave depression 240 collapses. The natural gas sample contained in the concave depression 240 passes through the center bore of wafer 231 and seal 233 and exits the sample chamber 228 through sample outlet 235.
A one-way valve 262 is in fluid communication with sample chamber 228 at the closed end of cylinder 232 so that sample chamber 228 is connected through one-way valve 262 to a pipe 13 that leads to sample cylinder pipe 14. When the pressure in sample chamber 228 becomes sufficiently high to overcome the bias of one-way valve 262, the natural gas within conical depression 240 passes through one-way valve 262 and pipe 13 into sample cylinder 14.
When timer 11 directs solenoid 10 to cause timing valve 9 to close, the natural gas under pressure within pressure chamber 218 is vented to atmosphere through sample pump pipe 12 and timing valve 9. Under the bias of spring 224, plate 226 and diaphragm 212 move back to their normal unstressed positions. As plate 226 moves back to its unstressed position, piston rod 236 and piston 234 also move away from the closed end of cylinder 232.
As the piston 234 moves away from the closed end of cylinder 232, the compression of plug 238 is reduced. When the pressure in sample chamber 228 drops below the pressure required to open one-way valve 262, one-way valve 262 will close so that sample chamber 228 will be a sealed chamber in contact with the closed end of cylinder 232. Further movement of piston 234 away from the closed end of cylinder 232 causes conical depression 240 to move away from sealing contact with the closed end of cylinder 232 so that a new sample of natural gas from connecting pipe 2 enters sample chamber 228.
Sampling systems such as the sampler assembly 1 shown in FIG. 1 are typically located at the "exchange points" where companies buy and sell gas or at a "gathering station" where pipelines from several natural gas wells come together.
Traditionally, both "exchange points" and "gathering stations" have been located on land. However, in recent years more and more natural gas wells have been drilled by offshore drilling rigs that drill into natural gas reservoirs located below water. On offshore drilling platforms, everything related to the drilling operation and the housing of the workers must be contained on the drilling platform.
It typically costs more to build a relatively larger offshore drilling platform than a smaller one. Therefore, offshore drilling platforms are made as small as possible. As a result, space on an offshore drilling platform is a precious commodity. Consequently, it is desirable to make sampler systems as small as possible in order to avoid taking up unnecessary and costly space.
Although less of a problem on land, it is still desirable to make sampler systems as small as possible. This is because on land, as well as on offshore drilling platforms, smaller sampler systems take up less space in the meter sheds or other structures placed over the sampler systems to protect them from the elements and from tampering or damage. The smaller the sampler systems, the smaller the protective structures can be. Smaller protective structures typically cost less to build and transport. Therefore, it is desirable to minimize the size of the sampler systems on land as well as on offshore drilling platforms in order of minimize the cost of protecting the sampler systems.
An additional benefit of reducing the size of the sampler systems is that smaller size usually means less material is needed to make the sampler systems. Because less material is needed to make the sample assemblies, the cost of materials for a sampler assembly drops.
A benefit related to reducing the amount of material needed to make sampler systems is that the time required to machine and polish the smaller component parts is usually reduced. As a result, reducing the size of the sampler systems usually means a reduction in the time, and corresponding cost, of manufacturing the components of the sampler systems.
A further benefit of reducing the size of the sampler systems is that smaller sampler systems typically require less energy to power the sampler assembly during the sampling process than do relatively larger sampler systems. Typical prior art sampler systems get their power to perform the sampling operation from the pressurized natural gas from the pipeline that is being sampled. As a result of the sampling operation, the pressurized natural gas that has powered the sampling operation is vented from the sampler assembly. Typically, the amount of natural gas released per sample is about 0.1 cubic feet.
Government regulations are now reducing the amount of, and in some cases forbidding, the release of natural gas into the atmosphere. As a result, the natural gas that previously was released into the atmosphere must now be collected or otherwise disposed of. One way of disposing of the previously released natural gas is to burn the gas in a catalatic heater. Whether collecting the previously released natural gas or alternately disposing of it, it is desirable to minimize the amount of natural gas released from the sampler assembly. Reducing the size of the sampler systems usually results in smaller amounts of natural gas being expelled from the sampler systems during the sampler process. Smaller amounts of natural gas released from the sampler systems translates into less cost for disposing of the released natural gas. In contrast with the prior art, the present miniaturized sampler vents only approximately 0.005 cubic feet of natural gas per sample.
Besides the disadvantages of taking up increased space, costing more to shelter and more to make, and reducing the amount of natural gas released from the sampler systems, another reason to make sampler systems as small as possible, particularly as it relates to offshore drilling platforms, is to minimize the difficulty involved in transporting relatively large components of the sampler assembly to and from the sampler assembly. For example, a typical prior art sample pump alone is typically about 81/2".times.81/2" and weighs about 121/2 pounds. Often, transporting such a pump to an offshore drilling platform in a helicopter requires that an entire passenger seat be used to carry the sample pump. This means that in a typical four-passenger helicopter, only three passengers and a sample pump may be transported at one time. In such circumstances, it is clearly desirable to minimize the size of the individual components of the sampler assembly, particularly the sample pump to minimize the difficulty presented in transporting the pump. In contrast with the prior art, the present miniaturized sampler weighs approximately two and one-fourth (21/4) pounds and is about 41/2".times.41/2".
As mentioned above, it is desirable to minimize the size of the sample pump 3 as much as possible. In this regard, one problem with the prior art pump shown in FIG. 2 is that flange 210 extends away from the main body of the respective covers 206, 208 by a significant distance, labeled "A" in FIG. 2. Since the function of flange 210 is to bind the two halves of covers 206, 208 together and form a gas tight seal, it is desirable to minimize the space needed to bind and seal the two sides of covers 206, 208 together in order to minimize the size of the sample pump 3.